SergeySlukin

<?php
function getRows($file) {
    $handle = fopen($file, 'rb');
    if ($handle === false) {
        throw new Exception();
    }
    while (feof($handle) === false) {
        yield fgetcsv($handle);
    }
    fclose($handle);
}

foreach (getRows('data.csv') as $row) {
     print_r($row);
}

class AuthorController extends Controller {
    public function actionIndex() {
        $authors = Author::find()->select(['author.id', 'author.name', 'books' => 'count(*)'])
            ->leftJoin('book', 'author.id = book.author_id')
            ->groupBy('author.id')->asArray()->all();
        return $this->render('index', ['authors' => $authors]);   
    }
}

foreach($authors as $author){
  echo '<h2>'.$author['id'].') '.$author['name'].'</h2>'; // 1) Иван И.И.
  echo '<p>Книг: '.$author['books'].'</p>'; // Книг: 17
}